Avoid loading collections when not needed

Collection loading logic was a bit disjointed between super- and
sub-class, this puts it one place, and makes sure we won't load
the collection unless we're going to actually create the activity

This is the final part that Fixes #4987

AnkiDroid/src/main/java/com/ichi2/anki/AbstractFlashcardViewer.java

@@ -823,8 +823,6 @@ protected void onCreate(Bundle savedInstanceState) {
 
         View mainView = findViewById(android.R.id.content);
         initNavigationDrawer(mainView);
-        // Open collection asynchronously
-        startLoadingCollection();
     }
 
     protected int getContentViewAttr(int fullscreenMode) {

AnkiDroid/src/main/java/com/ichi2/anki/Previewer.java

@@ -39,16 +39,19 @@ public class Previewer extends AbstractFlashcardViewer {
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         Timber.d("onCreate()");
+        super.onCreate(savedInstanceState);
+
         mCardList = getIntent().getLongArrayExtra("cardList");
         mIndex = getIntent().getIntExtra("index", -1);
         if (mCardList.length == 0 || mIndex < 0 || mIndex > mCardList.length - 1) {
             Timber.e("Previewer started with empty card list or invalid index");
             finishWithoutAnimation();
+            return;
         }
-        super.onCreate(savedInstanceState);
         showBackIcon();
         // Ensure navigation drawer can't be opened. Various actions in the drawer cause crashes.
         disableDrawerSwipe();
+        startLoadingCollection();
     }
 
     @Override

AnkiDroid/src/main/java/com/ichi2/anki/Reviewer.java

@@ -63,13 +63,14 @@ public class Reviewer extends AbstractFlashcardViewer {
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         Timber.d("onCreate()");
+        super.onCreate(savedInstanceState);
 
         if (Intent.ACTION_VIEW.equals(getIntent().getAction())) {
             Timber.d("onCreate() :: received Intent with action = %s", getIntent().getAction());
             selectDeckFromExtra();
         }
 
-        super.onCreate(savedInstanceState);
+        startLoadingCollection();
     }
 
     private void selectDeckFromExtra() {